Methods for dust control on saline dry lakebeds using minimal water resources

ABSTRACT

A method for controlling dust on a saline lakebed is disclosed comprising the steps of commencing the flooding of a wetting basin, testing to determine if there is a sufficient level of salts which when flooded will produce a brackish solution, testing the temperature of the lakebed substrate and curtailing further flooding of the lakebed depending on the substrate temperature.

This patent application is a divisional of non-provisional patentapplication Ser. No. 13/157,244, filed on Jun. 23, 2011, which claimedpriority to non-provisional patent application Ser. No. 12/841,971 filedJul. 22, 2010 which claimed priority to U.S. Provisional PatentApplication Ser. Nos. 61/228,271 entitled “System and Method for Use ofNatural Brine To Prevent Fugitive Dust Using Minimal Water,” filed onJul. 24, 2009; U.S. Provisional Patent Application Ser. No. 61/254,112entitled “System and Method for Use of Natural Brine to Prevent FugitiveDust Using Minimal Water,” tiled on Oct. 22, 2009; U.S. ProvisionalPatent Application Ser. No. 61/326,468 entitled “Chloride Salts WithDivalent Cations Provide Temporary Surface Stabilization in SalineSystems Dominated by Sodium,” filed on Apr. 21, 2010; and U.S.Provisional Patent Application Ser. No. 61/358,249 entitled “ChlorideSalts with Divalent Cations and Polyacrylamide Provide Temporary SuthiceStabilization in Saline Systems Dominated by Sodium,” flied on Jun. 24,2010.

Each patent application identified above is incorporated herein byreference in its entirety to provide continuity of disclosure

BACKGROUND AND SUMMARY

The present invention relates generally to the field of ecologicalmanagement and more particularly to the field of dust control orabatement of saline soils dominated by sodium salts using minimal waterresources. One embodiment of the invention was developed for the bed ofOwens Lake in Eastern California (FIG. 1) that is dominated by carbonateand sulfate salts of sodium; however, the embodiment described herein isapplicable to any environment that presents salt chemistry similar tothat within the Owens Lake bed, including for example, other saline drylakes or sumps receiving and concentrating water from agriculturaldrainage.

Soils enriched with sodium carbonate and sodium sulfate throughagricultural drainage, similar salty beds exposed due toanthropomorphically-changed hydrology (like the Owens Lake), and naturaldry lakebeds with shallow groundwater connection are prone to createlarge sources of airborne dust that can cause health and safety hazardswithin the surrounding region. Owens Lake was the historic terminus ofthe Owens River that was diverted for export by the City of Los Angelesresulting in desiccation of the lake early in the last century.

The Owens Lake bed is highly saline with some locations containing up toaround 60% by weight of the salts sodium carbonate, sodium bicarbonateand sodium sulfate. When these salts are dissolved by rain or snowduring cold temperatures, they re-precipitate as decahydrate thatincorporates 10 molecules of water for each salt molecule. Thetemperatures governing re-precipitation that incorporates decahydrateoccurs at about 50 degrees Fahrenheit for sodium carbonate salts andabout 65 degrees Fahrenheit for sodium sulfate salts.

Re-precipitation of salts in the decahydrate form causes crystals toswell 4-5 times their volume. Decahydrate salt crystals lose watermolecules in alternating warm and cold temperatures in winter andespecially during warm sunny days. This process destroys soil cohesionand renders the surface easily lofted by only moderate winds of about 15miles per hour. This salt-phase-change mechanism is largely responsiblefor the severe dust problems at Owens Lake, prompting it to be therecognized as the largest single dust source in the United States.

Federal and state laws mandate that the City of Los Angeles Departmentof Water and Power (LADWP) perform dust control for Owens Lakerecognized as the former single largest source of respirable particulateair pollution in the United States. Through several decades of intensivestudy, three dust control methods have been identified by the agencyresponsible for monitoring and enforcing dust control: wetting thesurface, covering the surface with vegetation, or covering the surfacewith gravel. Of these three, only surface wetting, in constructedartificial (man-made) wetting basins has been able to accomplish dustcontrol within the time and scale required.

Unfortunately, wetting of the Owens Lake surface is using enormousamounts of water—LADWP uses four feet per year to plan for the requiredwater application for dust control through the dust control season. Thetotal amount of water use can greatly exceed 100,000 acre feet per yearon over 40 square miles of the lakebed—this amount is sufficient waterto supply about 400,000 families. Within the critically water-shortsemi-arid southeastern California region, this annual consumption ofwater for dust control is not sustainable.

During the process of desiccation, naturally saline Owens Lake waterconcentrates to form an evaporite deposit in the lakebed's lowesttopography. The evaporite deposit covers about 34 square miles, has anaverage depth of about 2.6 feet and varies in thickness from a fewinches to about 9 feet (FIG. 2). The evaporite deposit consists ofprecipitated salts and salt held in concentrated aqueous solution. Thisaqueous solution is brine, dominated by sodium chloride that remains insolution because it is much more soluble than sodium sulfate and sodiumcarbonate at common ambient temperatures at the Owens Lake. The sodiumchloride-rich brine isolates the potentially emissive salts of sodiumcarbonate and sodium sulfate from atmospheric desiccation, therebyprotecting the source deposit from being dust emissive. The term“wetting basin” is synonymous with “dust control wetting basin” and is apolygonal area enclosed by berms flooded with water to control dustemissions from the lakebed as seen in FIG. 2.

The present invention includes systems and/or methods that will protectthe surface from releasing dust, use present infrastructure, ifavailable, that was built to provide surface wetting (or at other sites,create such infrastructure) with minor modification, consume minimalwater resources for startup, and consume little or no additional waterfor maintenance. Each of three methods provides the surface protectionby working with the natural properties of the salts present within theOwens Lake system. In one of the methods a different type of salt isimported that, with another ingredient, works to stabilize the surface.

The embodiments of the present invention comprise three methods:

-   -   (1) The use of brine from salt mined, dissolved and moved from a        natural source deposit to create salt deposits within        reconfigured wetting basins, including basins that were        originally created for dust control using fresh water flooding.        These created salt deposits will form a “Brine Membrane” that        mimics the stable non-dust-emissive source deposit by having        horizontal beds of precipitated salts with the most soluble        salts retained within a sodium chloride brine solution that        bathes and caps the precipitated horizontal beds of salt        beneath. The control of evaporation by the Brine Membrane        maintains the deposit in a wetted state (non-desiccated,        non-dust emissive).    -   (2) The use of small quantities of polymer and divalent cation        salts of chloride (for example calcium chloride) to stabilize        emissive areas of exposed lakebed, not yet treated by        construction and flooding of wetting basins. This is called the        “Interim Solution” since it allows for later conversion to a        wetting basin or to conversion by the Brine Membrane method once        the wetting basin is constructed. The Interim Solution can        provide stability on very large areas and can provide protection        for wetting basins that were formerly filled with fresh water        for dust control.    -   (3) The use of measurements of soil temperatures to predict when        the soil temperature within flooded wetting basins reaches and        exceeds the governing temperature when the salts of sodium        sulfate and carbonate will no longer undergo phase changes that        would render a desiccating surface prone to windborne dust        emission. This method is called “Springtime Conservation”        because it curtails water to control the dust in wetting basins        as the temperatures warm during the spring.

All three of these methods provide a transformation from the currentwasteful practice of flooding emissive surfaces with large amounts ofwater that evaporates annually, while protecting the lakebed surfacefrom windborne dust emission.

A brief description of the three methods follows.

Brine Membrane

The Brine Membrane method of the embodiment may be summarized asrequiring dissolution and movement of large quantities of salts from asource deposit to prepared wetting basins where it will form similarsalt deposits that will replace fresh water, transforming the wettingbasins from a wasteful byproduct of evaporation to a non-waterconsuming, non-dust emissive surface. Sodium chloride, the salt thatprovides the protective mechanism responsible for retaining thenon-emissive qualities of a lakebed source deposit, may be present inlimited but sufficient quantities, if managed correctly. Thus, managingthe sodium chloride resource between the salt beds created within thewetting basins and the source deposit ensures that this mineral is notdepleted in either environment so that both are protected fromdesiccation and the salt masses remain non-dust-emissive. Because thesalt bed that is created tends to remain wetted perpetually, the BrineMembrane method qualifies as shallow flooding that is recognized as aBest Available Control Measure, approved for application to control dustfrom the Owens Lake bed.

The Brine Membrane concept arose out of scientific discoveries at OwensLake during study of evaporation from the evaporite deposit as reportedby the inventor and others in an article entitled “Floating brinecrusts, reduction of evaporation and possible replacement of fresh waterto control dust from Owens Lake bed, Calif.,” Groeneveld, D. P.,Huntington, J. L. and Barz, D. D., Journal of Hydrology, 392 (2010)211-218, published Oct. 15, 2010. The following two paragraphs are thesummary and conclusion from that paper.

Owens Lake, Calif., a saline terminal lake desiccated after diversion ofits water source, was formerly the single largest anthropogenic sourceof fugitive dust in North America. Over 100 billion m⁻³·yr⁻¹ of freshwater are projected to be used for mandated dust control in over 100 km²of constructed basins required to be wetted to curtail emissions. Anextensive evaporite deposit is located at the lake's topographic low andadjacent to the dust control basins. Because this deposit is non dustemissive, it was investigated as a potential replacement for the freshwater used in dust control. The deposit consists of precipitated layersof sodium carbonate and sulfate bathed by, and covered with brinedominated by sodium chloride perennially covered with floating sa crust.Evaporation (E) rates through this crust were measured using a staticchamber during the period of highest evaporative demand, late June andearly July, 2009. Annualized total E from these measurements wassignificantly below average annual precipitation, thus ensuring thatsuch salt deposits naturally remain wet throughout the year, despite thearid climate. Because it remains wetted, the evaporite deposit has thepotential to replace fresh water to achieve dust control at near zerowater use.

Floating salt crusts that cover NaCl-dominated brine are the expectedsurface condition for the natural evaporite deposit at Owens Lake. Thesefloating crusts reduce evaporation to levels less than precipitation,thus ensuring that the evaporite body remains wetted at all times.Moving salts from an existing evaporite deposit to the dust controlbasins may, therefore, offer a viable replacement for the fresh waterused for dust control on the dry lakebed. Using the adjacentnon-dust-emissive natural evaporite deposit as a model, salt depositscreated in the dust control basins could be engineered to containsubstantially equal proportions of precipitated salts of Na₂SO₄ andNa₂CO₃, below, capped by a layer of NaCl-dominated brine. Salt crustswould form atop this supernatant brine layer to reduce annual E to lessthan annual precipitation, thus ensuring that the engineered saltdeposits would also remain wet and non-emissive. Once established, thenatural properties of salt deposits modeled upon the natural deposit mayenable complete dust control with near zero additional fresh water.

These scientific findings prompted additional research that concludedthat creation of the Brine Membrane over large areas of the Owens Lakebed would introduce profound water conservation for dust control. Thisresearch also found that large-scale application of the Brine Membraneis practical because there are sufficient salts within the evaporitedeposit to treat a large proportion of the existing dust control wettingbasins without creating additional fugitive dust sources, and that thetechnology required can be adopted for Brine Membrane implementation.The Brine Membrane effectively transforms surfaces of the Owens Lakebedinto stable non-emissive salt beds using a minimum of water resources.

Another scientific finding concerning the Brine Membrane was that theproperties of the NaCl-dominated brine are what enable the crusting tofloat atop the brine. The density of the brine solution is increasedbecause it includes ions of carbonate and sulfite. The high density ofthe brine, in turn, permits the NaCl crusts to float atop the brine.Floating, this crusts of salt are what reduce evaporation and thesecrusts will form but not perpetually float on top of pure solutions ofNaCl.

Interim Solution

In conditions where the lakebed surface has been identified as emissivebut where wetting basins have not yet been created, a second embodimentof the invention called the Interim Solution can be implemented; thisembodiment of the method utilizes a mixed solution comprisingpolyacrylamide (PAM) and calcium chloride or other divalent cationchloride salt. When applied onto the lakebed surface, the cation, forexample calcium, creates precipitates with the sulfate and carbonateions that will remain stable in a high pH lakebed environment (as gypsumand lime). Small quantities of PAM serve to tack these precipitatestogether electrochemically creating a surface skin that is resistant towind erosion and weather-induced deterioration that is effective for oneor more dust “dust season”—the dust season has been defined for theOwens Lake example, as the period between October 1 and June 30 of eachyear. Although the Interim Solution is anticipated to be temporary, itis comparatively inexpensive, and can be reapplied as necessary. TheInterim Solution transforms a surface that gives rise to fugitive dustto a stable non-emissive surface using minimal water resources.

Springtime Conservation

There are conditions that may obviate the conversion of an existingwetting basin by the Brine Membrane method—for example where the wettingbasin may serve an alternative function as a wildlife habitat or wherethe potential rate of percolation brine loss from the basin would beunacceptably high and the use of fresh water must be continued. Underthese conditions, Springtime Conservation provides a third waterconserving embodiment of the method of the present invention. SpringtimeConservation can potentially conserve water by safely curtailingsupplies of water to wetting basins during the last two months of thedust season in May and June coinciding with intensive evaporation.

Current regulations that set forth the dust season at Owens Lake arebased upon observations of the annual period that dust is typicallyreleased, and requires that water be supplied to the wetting basinsthrough this period, each year until the end of June. Rainfall duringthe warmer seasons is known to create competent “summer crusts” thatremain until the surface either becomes physically damaged by wind orother mechanical disturbance or undergoes wetting during the winterfollowed by salt phase-induced destruction of soil cohesion as describedabove. The June threshold arose because summertime winds are generallyinsufficient to cause dust emission from those portions of the OwensLake bed that emitted dust during the winter and spring. The key tore-stabilizing emissive portions of the lakebed each summer is to createa summer crust following rainfall during warm weather. Such rewettingand crust formation typically occur each year because at least somerainfall occurs during the warmer months.

The creation of a summer crust protects lakebed surfaces from dustemissions until a wetting basin is again flooded for dust control inlate summer in preparation for the new dust season. The point-in-timewhen water supplies to wetting basins can be safely curtailed eachspring is defined by soil temperatures that govern the phase changes ofsodium sulfate and sodium carbonate salts. If soil temperatures aresufficiently warm, above about 50 degrees Fahrenheit for sodiumcarbonate and above about 65 degrees Fahrenheit for sodium sulfate, andif sufficient salts are present, as indicated by brackish water withineach wetting basin, the formation of a summer crust will occur. Summercrusts are stable because the salts precipitate with few inclusive watermolecules in the crystalline matrix thereby forming a bridge forgrain-to-grain contact within the soil. When dry, summer crust isextremely hard and durable.

Springtime Conservation is a method embodiment that curtails waterdelivery to the wetting basin when temperatures are safely forecasted toinduce summer crust formation. This method, favored for wetting basinsthat are undesirable for conversion to Brine Membrane can still savealmost one third of the water that is used within such wetting basins.Springtime Conservation transforms the dust control wetting basins inthe last two months of the dust season from a highly evaporative wettedsurface that requires constant resupply with water into a drynon-emissive surface, thereby conserving significant water resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises three maps to illustrate the location of Owens Lake inCalifornia in the United States; and

FIG. 2 is a Landsat view of Owens Lake, modified by the inventor with adashed line to show the approximate location of the evaporite depositand surrounded by dust-control wetting basins (dark polygons), taken inlate Spring, 2009.

FIG. 3 is a flowchart depicting an overview of the system to place theembodiments in context with respect to the three methods for dustcontrol using minimal water resources;

FIG. 4 is a flowchart of an embodiment depicting a method in accordancewith one aspect of the present invention, a Brine Membrane that is astable, non-dust-emissive salt bed with annual evaporation rates lessthan annual rainfall;

FIG. 5 is a schematic cross-sectional view of a lakebed illustrating thewater savings attributable to aspects of the present invention;

FIG. 6 is a graph showing temperature-dependent single salt solubilityfor the dominant salts in the Owens Lake as a guideline for managingwater temperature required to dissolve the major salt species mined fromthe source deposit for establishing the Brine Membrane within thedust-control wetting basins;

FIG. 7 is a flowchart of an embodiment depicting a method in accordancewith another aspect of the present invention, the Interim Solution, thatis, a temporary application to stabilize dust-emissive surfaces usingsalt and polymer chemistry;

FIG. 8 is a flowchart of an embodiment depicting a method in accordancewith still another aspect of the present invention, SpringtimeConservation, that uses measurements of soil temperature to decide whencurtail water supply to wetting basins in the spring;

DETAILED DESCRIPTION

As will be appreciated by those skilled in the art, aspects of thepresent invention are described in detail with reference to severalembodiments of methods that transform dust-emissive portions of salinesoils dominated by sodium salts, such as a dry lakebed, including, butnot limited to, the Owens Lake bed surface, to provide complete dustcontrol while minimizing water use,

Method for Selection of Optional Dust Control Methods

As shown in FIG. 3, a method of dust control in accordance with oneembodiment can begin at START (S100). At step S102 it is determinedwhether or not there are dust emissions from a discrete region or site,such as a dry lakebed, by monitoring air quality at step S104. As usedherein, the “dust” includes any particulate matter that is expelled orcan arise from the earth surface into the atmosphere by natural winds orby wind artificially and inadvertently caused by vehicle passage on theearth surface where it can be inhaled by humans or other animals.

In the event that there is no prevailing dust problem, then the methodof the preferred embodiment returns to air quality monitoring step S104awaiting potential dust conditions. Those of skill in the art willappreciate that implementation of the embodiment methods describedherein will likely result in mitigation of identified dust emissions,but that all surfaces of concern, whether subject to control, or not,should be continuously monitored for any deterioration resulting in dustpollution. Step 104 is the responsibility of the agency that monitorsand enforces air quality of a lakehed and surrounding region.

Step S106 of the method embodiment queries whether there is an existingdust control wetting basin at the site for dust control. If the responseis affirmative, then the method proceeds to S108 that queries whetherthe wetting basin could be converted to Brine Membrane. The decision atS108 is made in consideration of whether (1) seepage losses are high andtherefore potentially problematic for retention of the bathing sodiumchloride brine for the Brine Membrane method that would protect the saltbed mass from desiccation, (2) it is desirable to convert the wettingbasin to Brine Membrane control, but such control must be postponed dueto priorities and resources, or (3) there are competing uses for thewetting basin such as a wildlife habitat that would render the BrineMembrane method less desirable. If the response to query S108, whetherto convert an existing wetting basin to Brine Membrane is affirmative,then the method of the embodiment proceeds to step S120 which refers toFIG. 4, a continued description of the embodiment, described in detailbelow.

If the response to query S108 is negative for any one reason, then themethod of the embodiment proceeds to S114 that queries whether theexisting wetting basin can be treated to curtail and conservelate-season water delivery using the Springtime Conservation method. Ananswer in the affirmative passes the process to step S170 of FIG. 8 thatdescribes Springtime Conservation. A negative reply to S114 indicatesthat the wetting basin is being managed by some other criteria wildlifehabitat, for example.

Returning to S108, and a no answer for whether the existing wettingbasin should be converted to Brine Membrane, an alternate pathway leadsto the query at S118 for determining whether wetting may be discontinuedfor water conservation. An answer in the affirmative leads to S150 thatinvokes using the Interim Solution. A no answer to query S118 leads toSpringtime Conservation. Hence, not converting an existing wetting basinto Brine Membrane leads to management to retain wetness (S116), use ofInterim Solution to stabilize the surface or to Springtime Conservation(S170).

Returning to decision block S106, if there is no existing wetting basin,then the method of the embodiment proceeds to step S110 that querieswhether a wetting basin should be created. If the response to S114 isnegative, then the method proceeds to step S150, referencing FIG. 7 anda continued description of the Interim Solution method, described indetail below.

Brine Membrane Method

FIG. 4 implements the decision made at step S108 to convert an existingwetting basin to Brine Membrane. The first step at S124 reconfigures theexisting wetting basin so that the basin requires a much lower volume ofsalt to create a stable bed than the volume of fresh water previouslyused to control dust. This reconfiguration is shown on FIG. 5 where anexisting wetting basin, indicated at 10, covering an area of lakebed 12,consists of an existing main berm or a main berm 14 that encloses adepth of water when the wetting basin is filled to capacity 16 toprotect the lakebed from dust emissions. To reduce the volume necessaryto file the wetting basin, interior berms 18 are built that tower thedepth required to cover the lakebed, producing much shallower depth thanthe original wetting basin 20. Reconfiguring the wetting basins, therebyconserves salt and saves money, energy, time, and water in mining,transporting and establishing the Brine Membrane.

Step S140 of the method embodiment creates hot water to dissolve thesalts mined from the evaporite deposit as indicated in step S142. Hotwater can be generated through passive solar or other means and is anecessary step that will permit rapid dissolution of the salts,especially sodium carbonate and sodium sulfate whose solubilities arehighly temperature-dependent. In FIG. 6 single salt solubility for majorsalt species, indicate that the effective temperature to bring sodiumsulfite and sodium carbonate into solution should optimally be above 25degrees Celsius (77 degrees Fahrenheit), necessitating heating. Asindicated in FIG. 6, those skilled in the art will appreciate thatenclosing, piping or otherwise transporting brine solutions nearsaturation run the risk of massive precipitation if the temperaturedrops below the solubility point for these salts. Once plugged byprecipitated salts, such piping is generally a total loss. Hence, atFIG. 4, block S144 is a step that calls out dilution of the brine sothat it can be safety transported. The imported brine solution fromblock S144 can be applied in step S126 to the wetting basin by meanssuch as flooding, or other suitable means for dispersing liquidsolutions upon a surface.

In another alternative to the method of the embodiment, sodium chloridemining and transport is managed so as to protect salt masses fromdesiccation and becoming sources of fugitive dust, either within thesource deposit or where created within the wetting basin. The method ofmanagement includes control of predetermined target ratios of the sodiumchloride salt to other salt ion species, including sodium carbonate,sodium bicarbonate and sodium sulfate, in a ratio that lessens thepotential for depletion of sodium chloride within the source deposit.

In another variation of the method of the Brine Membrane embodiment atS126, the brine solution can be applied at the lowermost portion of thewetting basin in order to: (1) add the brine in a manner that willminimize the ratio of the surface area to the depth so as to slowoverall evaporation during filling, (2) reduce the potential for rillerosion of the lakehed substrate, and (3) help achieve better mixing ofthe salts such that the Brine Membrane method provides continuous,stable salt beds.

Following application of the brine solution to the wetting basin in stepS126, step S128 of the method allows evaporation, and consequentconcentration and precipitation of the salts from the brine solutioninto stable horizontal beds of sodium carbonate, sodium bicarbonate, andsodium sulfate capped by a protective layer of brine that is dominatedby sodium chloride, thereby creating the Brine Membrane. In thisoperation, sodium chloride will remain in solution because it is moresoluble over the range of ambient temperatures within the lakebed thanthe other common sodium-dominated salts as indicated in FIG. 6.

In step S130 of the method of the embodiment, a query is made as towhether the flooding of the wetting basin has produced the desiredstable condition of the Brine Membrane. If the response is affirmative,then the method of the embodiment proceeds via S132 to stepS104—continuous future monitoring. If the response is negative, then themethod proceeds to step S148 in which the wetting basin is refloodedwith water at a predetermined time that provides the correcttemperatures for precipitation of sodium salts of carbonate, bicarbonateand sulfate, for example, the autumn season when seasonal cooling willcreate this condition. Additional salts may need to be added byimplementing step S148 to achieve the correct depth and/or mix of saltsin the wetting basin. Missing the desired stable endpoint by the BrineMembrane method in the horizontal beds of precipitate instead, cancreate an undesirable condition of spatial fractionation of salt specieswhere potentially dust-emissive salts are exposed to the atmosphere.This can occur if the evaporation of the water from the brine is highwhile the wetting basin is filling and if the brine is run acrossshallows with very high evaporation rates. This factor can also beremedied at the time of brine entry by monitoring, and increasing theproportion of water within the brine. Also, filling the wetting basin atthe downstream end will tend to prevent this condition from occurring.

It is assumed that for Brine Membrane conversion, potential seepagelosses and static water table levels will have been measured andunsuitable portions of the lakebed with high seepage rates and/or deepwater tables will have been avoided. However, in the event that theseepage losses from the wetting basin cause the reduction of asignificant portion of sodium chloride-dominated brine that percolatesfrom the wetting basin, sodium chloride brine can be recharged directlyfrom solutions that develop atop the source deposit each winter due todirect precipitation and/or runoff onto the source deposit from regionaldrainage subject to understanding and managing the overall sodiumchloride resource in evaporite deposit. The same site infrastructureused for the steps in FIG. 4 can be used to resupply the sodiumchloride, mixed with other dominant salts, if desired, to maintain thebrine membrane thereby protecting the surface from dust emissions whilecommitting only a minute fraction of the fresh water formerly used fordust control. Monitoring and understanding the system-wide balance ofsodium chloride is in order to harvest and export the sodium chloridewhile protecting the source deposit from desiccation.

Interim Solution Method

Referring back to step S110 where an area of the lakebed was identifiedas dust-emissive, did not yet have a wetting basin, our was planned toreceive a wetting basin, the means for protecting the surface called forthe Interim Solution embodiment in FIG. 7, that starts at S152 andcomprises application of an aqueous compound to provide temporarycontrol of dust. In the Interim Solution method, a dilute aqueoussolution, containing one or more divalent cation chloride salts, forexample, readily-available salts of calcium chloride or magnesiumchloride, and a dissolved portion of an anionic polyacrylamide (PAM),are mixed together to form a “mix solution.” Other suitable salts andpolymers can be used in conjunction with or as substitutes for thedivalent cation salts and PAM polymer noted herein.

The mix solution can be applied directly onto the dry dust-emissivesurface to be treated in step S156, such as a lakebed that containssodium carbonate and sodium sulfate. The mix solution will dissolve thesalts in the lakebed and the divalent cations will form stableprecipitates of carbonate (limestone) and sulfate (gypsum). Sodiumchloride is a byproduct of this reaction that remains in solution withinthe soil matrix where it will tend to migrate to the surface of thewetted lakebed with capillarity and evaporation to form thin sodiumchloride crusts that function to reduce evaporation. PAM functions toelectrochemically tack the precipitates and clays of the surfacetogether, increasing surface stability to resist the effects of wind andweather.

After application of the mix solution, the product of the InterimSolution method is tested to determine whether it has protected thesurface from wind erosion in step S158. If so, the embodiment of themethod proceeds to step S146, that returns to step S104 calling forcontinual monitoring of all lakebed surfaces to ensure that correcttreatment has occurred and that dust is not released. If, however, theanswer to query S158 is no, the surface is not properly protected,reapplication may be made. With each reapplication, the surface crustingwill become more resistant to wind erosion and remain intact for longerperiods.

Formulation of the mix solution may vary depending upon the dry surfaceto be treated and may require a pretreatment with dilute sodiumcarbonate and sodium sulfate salts. For example, certain substrates thatmake up the Owens Lake bed are dominated by coarse sands, particularlyin the region where the Owens River and other tributary inflows debouchonto the lakebed. Because these sands may have been leached byprecipitation over many decades, they commonly contain lowconcentrations of the dominant salts of Owens Lake, sodium carbonate andsodium sulfate and so, the mix solution, formulated to bond withdominant salts to stabilize the soil, may not be available in optimalsupply for this stabilizing reaction. These dry sandy soils often blowand emit dust and in this case, such sands can become more stable iffirst provided with a pretreatment of Owens Lake native brine that isrich in sodium carbonate and sodium sulfate to then bond with the mixsolution to provide the grain-to-grain bridging for holding the surfacesand in place against wind and weather. The majority of the Owens Lakebed is fine textured and enriched with sodium carbonate and sodiumsulfate and so should not need such added pretreatment.

Though not required for the mix solution to work, field tests have shownenhancement for the stabilizing effects of this method when the surfaceis compacted prior to application. A person skilled in the art willrecognize the dynamic nature of a dust-emissive lakebed and thenecessity to tailor the application rate and concentration of the mixsolution to the substrate to best stabilize the surface,

Springtime Conservation Method

Directing attention back to the flowchart in FIG. 3, in decision blockS108 after determining in step S106 that there is an existing wettingbasin that may be converted to a salt bed in step S108, but a brinemembrane solution is not acceptable, the method passes to step S114invoking the Springtime Conservation. If no, then the management of thewetting basin is following some criterion other than water conservation,for example maintaining a wet condition for waterfowl. If the answer tothe query is yes, then the existing wetting basin can be subjected toanalysis for Springtime Conservation, a method embodiment as describedin FIG. 8, starting at step S172,

Step S174 determines, by testing, whether the wetting basin hassufficient salts present in the lakebed substrate to cause the waterreleased for dust control to become brackish—very salty, though not tothe extent of brine. Residual salts in the soil and the flooding waterare necessary for attainment of the desired end condition for SpringtimeConservation, a summer crust that is stabilized by salt crystals thatprovide grain-to-grain bridging that arms the soil against the action ofwind.

In the event that the answer is no, the salts can be recharged to thewetting basin in block S178; the salt recharging adds the salts that aremined, dissolved and imported at Step 176 from brine mining andgeneration in steps S140, S142 and S144 on FIG. 3. In the event that thetest result in step S174 is yes, then the process passes to step S178comprising a test for the soil temperature within the wetting basin. Ifthe soil temperature is either at, or forecasted to be at, the governingtemperature for the phase change of the dominant salts in step S180, theSpringtime Conservation method is invoked at step S182 and waterdelivery to the wetting basin is curtailed. This curtailment thenconserves the water that would be supplied until June 30, thus savingabout 32% of the water used for dust control through the entire October15 to June 30 dust season.

In the event that curtailment is invoked, the final step in theSpringtime Conservation method embodiment passes back in block S184 tostep S104 of FIG. 3 that provides for monitoring of the system.

Example Embodiment

Other features and embodiments of the present invention are describedherein with reference to the particular site of Owens Lake, Calif. Thesystem and methods of the embodiments are adapted for use in dustcontrol wetting basins on the Owens Lake bed. The area of these basinswas 35.8 square miles measured on Apr. 22, 2011 by Landsat satellitedata used for monitoring wetting basin compliance.

The main goal of the Owens Lake embodiment is to control dust whileproviding nearly complete water conservation. Other goals are toimplement dust control for the lowest possible cost, as rapidly aspossible, and using a minimum of resources. For example, a method thatcompetes with the three conservation methods and that is under seriousconsideration, is the placement of four to eight inches of gravel atopengineering fabric—a method that may cost up to fifty million dollarsper square mile, require burning millions of gallons of diesel fuel.Once gravel is in place it is permanent, allowing no other options.

By rough estimate the total dust control area under shallow flooding,plus areas that have been identified for conversion to active dustcontrol, and areas that are a likely future targets for dust control, isabout 46 square miles. As will be discussed below, of this area, 10 to20 square miles might be managed as wildlife habitat that will require awater supply irrespective of conservation. That leaves between 26 and 36square miles to be managed for dust control and water conservation usingthe Brine Membrane and Interim Solution methods.

The Brine Membrane is the most expensive of the three methods and mustbe limited in its application to those areas with low potential forpercolation loss of the sodium chloride dominated brine resource. Acursory evaluation of the Owens Lakebed indicates that there are about16 square miles of dust control wetting basins, existing and planned,that have both very shallow water tables and very slow percolationrates. The likely required time for full conversion to 16 square milesof Brine Membrane is around five years, a rate dependent upon the rateof mining and dissolution of brine. This time period allows for carefulmeasurement and management of salts on the lakebed.

There is great interest for management and enhancement of wildlifehabitat that has become established on the Owens Lakebed as a result ofthe many square miles of shallow flooding. The areas that have beendiscussed range between 10 and 20 square miles. Limited opportunityexists to conserve water within wildlife habitat through application ofSpringtime Conservation, though the potential extent of that applicationis not yet known. Especially for habitat that is seasonal and used bymigratory waterfowl, Springtime Conservation may have applicability forthe period after the waterfowl have departed, still well before therecognized end of the dust season (June 30, each year).

On a residual area of 10 to 20 square miles that cannot be treated byBrine Membrane or serve as wildlife habitat, dust can be controlledusing the Interim Solution. Operational application of the Interimsolution can take place by gradually taking wetting basins out ofservice allowing them to dry and treating them with this spray oncoating. The efficacy of the Interim Solution is determined by theresidual sulfate and carbonate salts of sodium that remain in thelakebed. These minerals attach to the calcium from the calcium chloridein the mix solution with PAM to form insoluble limestone and gypsum.Thus, in the event that fresh water has leached areas of these nativesalts required for Solution to work, these salts can be replaced byspraying, or by adding salts to the wetting basin inflow prior toconversion to management with Interim Solution. The key to a well-runmanagement program employing Interim Solution will be an active effortto test conditions before treatment.

Within the Interim Solution PAM is weakly bonded electrochemically withthe calcium in the mix solution, and when exposed to the salts in thelakebed, creation of insoluble precipitates in the matrix of PAMmolecules provides an instant crust. Testing numerous formulations haveshown that highly dilute mix solutions (30× dilution of saturatedcalcium chloride) may actually work better than more concentratedformulas. Formulas may need to be varied according to the texture andsalt concentrations of the substrate that is treated.

Calcium chloride for the Interim Solution is mined approximately 200miles south of the Owens Lake and is available in sufficient quantitiesfor treatment of 10-20 square miles. Spray equipment developed foragriculture can be adapted to apply the Interim Solution. The largeareas for treatment do not need to converted to interim Solution controlall at once and can best be gradually phased in over several years. Thefirst areas to treat would be those identified to require some form ofdust control but with none currently in place. After dust is controlledby the Interim Solution on such identified uncontrolled areas first,then this method can be applied to dust control wetting cells that aregradually decommissioned.

Large areas of dust control can be accomplished using the InterimSolution method if it is employed in a “fire-brigade mode” where thetreatment is rapidly applied after the location is identified asemissive. Over time, some locations may receive repeated treatment.Retreatment is anticipated to create highly stable surfaces.Pre-treatment may be warranted for areas anticipated to be problematicbefore the dust season. Interim Solution can be applied any time of theyear, especially as a summer activity to ensure that all potentialdust-producing areas that have been identified during the previous dustseasons are treated and resistant.

Areas treated with interim Solution must be made off-limits for anyvehicular traffic that would compromise the stabilizing crust. Likewise,once treated, the application equipment should be moved in such a manneras to stay off of the treated areas. Thus, a treatment with InterimSolution will terminate by withdrawal of the spray equipment that treatsaccess ways as the last step so that no portions of the lakebed are leftwith broken crusts that are potentially emissive.

The regulatory agency for Owens Lake air quality maintains, and isimproving, a system of permanent, high resolution video cameras of thelakebed that are used for identification of dust producing areas. Thesecameras are operated daily and after dust has been detected, analysisprovides geocorrect maps of the dust sources that can be used to deployInterim Solution treatments with days of the event. Global positionsystem records of treated areas and identified areas will provideconfirmation of treatment as well as long-term electronic records forenhancing management.

A transition period of about five years is estimated to be required toachieve the 46 square miles of water-conserving dust control, if thisobjective is prosecuted intently. During transition to fullimplementation the wetting basins must remain flooded with fresh waterprior to conversion to Brine Membrane and Interim Solution.

The potential for using Springtime Conservation is especially greatduring the initial phase of the conservation program when the largestareas for dust control are using fresh water. After completion ofconversion to Brine Membrane and Interim Solution, the SpringtimeConservation method may still be of use, but only for that portion ofwildlife habitat where seasonal use has ended for example, wheremigratory wildfowl have migrated on leaving the managed wetting basinbehind. Even though its useful life may be limited, SpringtimeConservation can be placed into service rapidly and save significantwater during the transition period.

The water that can be conserved with these methods is immense. For thehigh conservation assumption, with 10 square miles remaining flooded aswildlife habitat, the potential savings for treating the residual 36square miles with Brine Membrane or Interim Solution will eventuallysave over 92,000 acre feet of water per year (calculated using 4 feet ofseasonal water application over 36 square miles). For the low estimate,assuming 20 square miles as wildlife habitat, would yield conservationon 26 square miles of the lakebed, or over 66,000 acre feet per year.Additional savings through application of the Springtime Conservationmethod could potentially deliver additional water conservation afterconversion, and play a significant role in water conservation during thetransition to full application of Brine Membrane and Interim Solution.

Of the three methods, the Brine Membrane is the most complex since itwill require management of the evaporite source deposit as well as thewetting basin target deposits. The source of the salts used to createthe Brine Membrane within wetting basins in the first embodiment comesfrom the source evaporite deposit whose mineral content is shown belowin Table 1. These data resulted from over one thousand samplingboreholes made into the source deposit by three mining companiesoperating on Owens Lake over the past half century. The average brinephase content in the evaporite deposit is 30% by weight and the solidphase is 70% by weight. Abbreviations are Na, sodium; CO₃, carbonate;HCO₃, bicarbonate; Cl, chloride; SO₄, sulfate.

TABLE 1 AVERAGE % WT. SOLID PHASE Na₂CO₃ 41.5 NaHCO₃ 25.0 NaCl 2.6Na₂SO₄ 12.4 Insoluble 9.1 H₂O 9.4 BRINE PHASE Na₂CO₃ 8.9 NaHCO₃ 0.2 NaCl18.0 Na₂SO₄ 4.5 H₂O 68.4

A sufficient quantity of salt exists within the source evaporite depositto supply all, or part of the existing approximately 36 square-milesurface of the wetting basins with salt deposits, while also maintainingin situ, sufficient salt in the existing evaporite deposit to protectthat surface from dust emissions. Following the methodology of the BrineMembrane embodiment ensures that salts from the source evaporite depositwould replace fresh water within the wetting basins in such a mannerthat the conditions created by the Brine Membrane in the Owens Lakewetting basins would maintain a stable non-emissive surface in the samemanner as the evaporite deposit.

The massive amount of salt required to be mined and moved to the wettingbasins for replacement of fresh water and the tendency for the limitedquantity of the sodium chloride ions to remain in solution requires thatexporting of the salts for creation of the Brine Membrane followsubstantially the same proportions of salts as in Table 1. This ensuresthat the sodium chloride is not depleted from the evaporite sourcedeposit. The protective crusting that controls evaporation is conferredby sodium chloride and this is important for both creating the BrineMembrane within wetting basins and for retaining such conditions withinthe mined and unmined portions of the evaporite deposit.

The Owens Lake climate, with three to four inches of rain and snowfalleach year is intensely arid and evaporation rates for fresh water exceedsix feet per year. Even so, the thin crusting that develops atop sodiumchloride dominated brine can reduce the annual evaporation rates tobelow the level of the annual total rain and snowfall received. Thespecial properties of the sodium chloride dominated brine in Owens Lakeenables support of a thin crust to remain floating atop the saturatedbrine beneath. The natural dissolution of small amounts of sodiumcarbonate and sodium sulfate in this sodium chloride dominated brinecauses an increase in the density of this liquid an that the crustremains floating, it can be demonstrated that such crusts can form onlytemporarily surface tension but then sink through the liquid ofsaturated solutions of pure sodium chloride.

The property of the sodium chloride-dominated brine that reducesevaporation atop the Brine Membrane is what confers its effectiveness asa dust control measure it rain and snow to enter and remain wet, nomatter how hot and dry the conditions. The agency responsible formeasuring and enforcing air quality at Owens Lake recognizes that, forpurposes of dust control, the brine membrane is the equivalent ofshallow flooding specifically because it retains the salt mass below ina hydrated state.

The principal salts of the Owens Lake are formed by cation sodium incombination with the anions of carbonate, sulfate and chloride. Sodiumsulfate and sodium carbonate change the hydration state due totemperature and water availability. To move the massive quantities ofsalts required in the Brine Membrane method across many square miles ofwetting basins, the source deposit may be mined mechanically. Because oftemperature-dependent solubility of both sodium carbonate and sodiumsulfate, the principal salt components within the source deposit,dissolving these salts will require heated water.

Passive solar collection is a convenient, potentially inexpensive andpractical method to generate sufficient hot water at the Owens Lakesite; however, other methods could be used to generate the hot water byburning fuel, especially during a cloudy day. Potential also exists forgenerating a certain amount of heated brine by flooding and drainingwetting basins, however, the insoluble fraction (Table 1) will tend toseal off the salt mass over time and this sealing must be overcome,perhaps through mechanical means such as scarification. Systems of dikedoff and mined panels can be used to store brine of variable salt contentthat can be blended to create the desired mix to be exported from theevaporite deposit. A number of mechanically mined panels are currentlylocated at the south end of the evaporite deposit. These panels arehighly stable against wind erosion and can serve as the model to protectthe evaporite deposit once it has been mined.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular terms “a” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of the stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements and specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the embodiments disclosed. Many modificationsand variations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theexample embodiments were chosen and described in order to best explainthe principles of the invention and its practical applications, and toenable others of ordinary skill in the art to understand the inventionwith its various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method for temporary relief of dust pollutionat a dry lakebed having multiple wetting basins spread over a largegeographic area and an adjacent evaporite deposit of precipitated salts,comprising: timing implementation of the method to the springtime;commencing water flooding of the dry lakebed wetting basins; testing theexisting lakebed substrate to determine if there is a sufficient levelof salts which when flooded with water will produce a brackish solution;if not, transport brine from the evaporite deposit to create a brackishsolution in which the total dissolved solids is between 1,000 and 10,000mg per liter; testing the substrate temperature to determine whether theexisting or forecast temperature is sufficient for effecting evaporationof the brackish solution; and if the temperature of the substrate issufficient, curtail further flooding of the lakebed.
 2. The method ofclaim 1 wherein sufficient substrate temperature is at least 50 degreesFahrenheit if the dominant salt is sodium carbonate.
 3. The method ofclaim 1 wherein sufficient substrate temperature is at least 65 degreesFahrenheit if the dominant salt is sodium sulfate.
 4. A method forrelief of dust pollution during the October-June dust season at the OwenLake, Calif. saline dry lakebed having multiple wetting basins spreadover a large geographic area and an adjacent evaporite deposit ofprecipitated salts including sodium carbonate and sodium sulfate and asodium chloride-dominated brine, comprising: timing implementation ofthe method to the period April through June; commencing water floodingof the dry lakebed wetting basins; testing the lakebed substrate todetermine if there is a sufficient level of precipitated salts,including sodium carbonate and sodium sulfate, which when flooded withwater, will produce a brackish solution; if not, transport brine fromthe evaporite deposit to create a brackish solution; testing thesubstrate to determine whether sodium sulfate or sodium carbonate is thedominant salt; testing the substrate temperature after determining whichsalt is dominant; if the dominant salt is sodium carbonate and thetemperature is above 50 degrees Fahrenheit, curtail flooding of thelakebed basins; and if the dominant salt is sodium sulfate and thetemperature is above 65 degrees Fahrenheit, curtail flooding of thelakebed basins.
 5. The method of claim 4 wherein the brackish solutioncomprises a salinity of dissolved salts between 0.5 and 30 parts perthousand.